Get WP Robot, hook up TBS and let'er fly. Does exactly what you just asked.
Get the RSS feed run it through full text rss first, then insert the feed into WPRobot, integrate it with The Best Spinner (easy to do) and off you go. You can hook up multiple RSS feeds like this too. You can even insert videos for your KW to post in same post, pictures whatever you name it. It will even post pictures of your girlfriend (just kidding).
free ones usually dont have good features & support.